This invention relates to novel 4,4-dihalohexahydrophthalic anhydrides of the formula ##STR3## and a novel 4-fluoro-1,2,5,6-tetrahydrophthalic anhydride of the formula ##STR4## Methods for preparing and utilizing these compounds are also disclosed.
The compounds of this invention are useful as chemical intermediates for the synthesis of various end products. In particular, 4,4-dihalohexahydrophthalic anhydride and 4-fluorotetrahydrophthalic anhydride are useful in the synthesis of 4-fluorophthalic anhydride, which in turn is useful for the preparation of aromatic ether and thioether anhydride curing agents, antioxidants and polyetherimide polymers. Examples of the utility of 4-fluorophthalic anhydride and the various prior art methods for the synthesis thereof are disclosed in U.S. Pat. Nos. 3,850,965 and 3,956,321. An alternate method for synthesizing 4-fluorophthalic anhydride directly from the 4,4-dihalohexahydrophthalic anhydrides of the present invention by simultaneous dehydrohalogenation and dehydrogenation is disclosed in a commonly assigned application of David Y. Tang entitled "Process for the Preparation of 4-Fluorophthalic Anhydride", now U.S. Pat. No. 4,517,372.
The following U.S. Pat. Nos. provide further background relative to the chemistry of cyclic anhydrides and halo-substituted cyclic anhydrides: 1,891,843 to Shaw et al; 2,391,226 to Clifford et al; 2,764,597 to Barney; 3,240,792 to Patrick et al; 3,346,597 to Acetis; 3,480,667 to Siegart et al; 3,819,658 to Gormley et al; 4,045,408 to Griffith et al; and 4,302,396 to Tsujimoto et al.
The preparation of tetrahydrophthalic anhydrides and the aromatization thereof by dehydrogenation under various conditions is known in the chemical literature. Skvarchenko et al., Obshchei Khimii, Vol. 30, No. 11, pp. 3535-3541 disclose the aromatization of chloro-substituted tetrahydrophthalic anhydride by heating with phosphorus pentoxide. In the aromatization process described, however, decarboxylation also occurs with the formation of the corresponding chlorosubstituted benzene compound. The preparation of tetrahydrophthalic acids and anhydrides and various methods for dehydrogenation and aromatization thereof are reviewed by Skvarchenko in Russian Chemical Reviews, Nov. 1963, pp. 571-589.
Bergmann, J. Amer. Chem. Soc., 64, 176 (1942) discloses the aromatization of tetrahydrophthalic anhydride products of Diels-Alder reactions. The author discloses that dehydrogenation occurs when the tetrahydrophthalic anhydride product is boiled in nitrobenzene. However, it is further disclosed that dehydrogenation does not occur when p-bromonitrobenzene, p-chloronitrobenzene, or m-dinitrobenzene in xylene is employed. Moreover, it has been found that when the dihalohexahydrophthalic anhydrides of this invention are dehydrogenated in nitrobenzene, a portion of the nitrobenzene is reduced to aniline. The aniline reacts with the anhydride group of either the starting material or product to form imides and thus lower the yield of desired product.
The preparation of 1-fluorocycloalkene from the corresponding 1,1-difluorocycloalkane by reaction with anhydrous neutral alumina is disclosed in Strobach et al., J. Org. Chem., Vol. 36, pages 818-820 (1971).
The preparation of 4-fluoro-1,2,3,6-tetrahydrophthalic anhydride is disclosed in U.S. Pat. No. 2,451,612. The reference discloses that this isomer can be prepared by the reaction of fluoroprene (2-fluoro-1,3-butadiene) with maleic anhydride. The compound is reported as the hydrolyzed fluorophthalic acid.
It is a principal object of the present invention to provide novel intermediate compounds which are useful in the synthesis of 4-fluorophthalic anhydride. It is another object of this invention to provide a commercially attractive synthetic route to prepare 4-fluorophthalic anhydride.